This invention relates generally to devices and apparatus used in controlling emissions as from industrial sources, and more particularly concerns electrically charged fog generating or throwing apparatus useful in inhalable particle control.
Although progress has been made in the past in controlling emissions from conventional industrial sources, air pollution regulator agencies are becoming increasingly concerned with the non-attainment of ambient total suspended particulate matter standards, due mainly to fugitive emissions from various sources. In the past, fugitive emissions have been of concern only from a nuisance standpoint, increasing soiling potential and decreasing atmospheric visibility only in the immediate vicinity of the source. It has also been recognized that inhalable particles (&lt;15 .mu.m), fine particles (&lt;2.5 .mu.m) in particular, have a dominant role in causing hazards to human health and degradation of visibility. The fine particles can remain in the atmosphere for extended periods and can be transported over long distances.
Indiscriminate spraying of large amounts of water has been the most common control melthod used in mines and other fugitive emission sources and it has been only marginally successful. In a mine atmosphere, 30-40% is the accepted value for the dust control efficiency of water sprays. However, even this method has problems with clogged water spray nozzles and the need for large quantities of water.
It has been known that industrial pollutants and naturally occuring fugutive dusts acquire electrostatic charges as they are dispersed into the air. It is also known that the charge on fine particles of fugitive emission is usually negative. Therefore, if oppositely charged water droplets are sprayed on the dust to be suppressed, the particles which collide with the charged droplets will agglomerate rapidly and settle out of the atmosphere. The collection efficiency of water sprays can be improved significantly if well-charged water droplets (fog) of approximately 20 to 200 .mu.m diameter can be generated. Commercially available instruments to generate charged fog use either a standard pressure-type or twin-fluid nozzle to atomize the water, thus necessitating a substantial supply of high pressure water or air for proper atomization. These types of nozzles have a tendency to clog if the water supply contains a high concentration of suspended salts.